1. Field of the Invention
The present invention relates to computer processing of optical skin pattern images to produce rolled skin pattern images, especially fingerprint images.
2. Description of Background Material
Over the years, the most commonly used technique for obtaining "rolled" fingerprints has been to apply ink to the tip of individual fingers and roll the inked fingertips at an appropriate location on an applicant card. While these inking procedures will usually provide satisfactory images, they have their drawbacks. The inking procedure is messy. Several attempts are often required in order to obtain an acceptable fingerprint. Perhaps even a bigger drawback of this systems is that the printed images are not easily adaptable to computerized storage and processing techniques, inhibiting cooperation and fingerprint data transfer between various police agencies.
Systems which optically or optically and mechanically generate fingerprint images are also in use. Several such fingerprinting systems are disclosed in Fishbine et al. U.S Pat. No. 4,933,976, Ruell German Pat. No. 3423886 Al, Becker U.S. Pat. No. 3,482,498, McMahon U.S. Pat. No. 3,975,711, Schiller U.S. Pat. Nos. 4,544,267 and 4,322,163, and Marcus U.S. Pat. No. 4,553,837.
Due to the compound curved nature of the fingerprint on a finger, it is difficult to optically obtain an image of the fingerprint, especially an image corresponding to a rolled fingerprint. Fishbine et al. discloses a method based on building a composite image from a plurality of arrays of slice data characteristic of adjacent and overlapping two-dimensional slices of the fingerprint image.
The other references rely on complex mechanical movement of the fingerprint receiving optics. The Ruell patent discloses a fingerprinting system in which a camera images a finger rolled across a contact plate. Contact sensors on the edge of the plate provide information representative of which portion of the contact plate the finger overlies. The result is a plurality of adjacent but not overlapping two-dimensional slices that are pieced together to form the fingerprint image.
The Schiller patents disclose an apparatus in which a finger pressed against a platen provides a fingerprint object which is scanned by an interrogating beam of collimated light. The beam is linearly displaced across the platen thereby maintaining a constant angle between the interrogating light beam and the plane of the object being scanned. The Marcus U.S. Pat. No. 4,553,837 discloses a finger processing apparatus which includes a cylindrical-segment platen which supports a finger. Optical scanning equipment scans the circumference of the platen in such a manner that the angle of incidence of a light beam on the fingerprint object remains constant. The Becker U.S. Pat. No. 3,482,498 discloses several embodiments of an optical apparatus for producing a rolled fingerprint image. The embodiment shown in FIG. 1A utilizes a plurality of prisms and light sources, and produces only an approximation of the ball and side ridges. The embodiment shown in FIGS. 2 and 3 utilize a mechanical system actuated by a rolling finger to move and position a light source.
While the fingerprinting systems disclosed in the Ruell patent, the Marcus patent and the Becker patent may be capable of optically providing a rolled fingerprint image, these systems are less than wholly desirable. The mechanical aspects of these systems are relatively complicated. As a result, discontinuities, stray artifacts and other irregularities can appear in the composite image due to loss of focus or errors in merging the slices. The Fishbine et al. patent overcomes these problems but at the cost of requiring added computational power.
It is evident that there is a continuing need for improved optical fingerprinting systems. A system which can optically generate rolled fingerprint images in real time with limited computational requirements is desired. The system must of course be accurate and reliable.